One store in Guatemala City after LED lighting installation (before is below), photo: Walmart StoresThe following is a guest post from Charles Zimmerman, vice president of international design and construction at Walmart.

Today it takes a lot of coal, natural gas, wind, solar and other energy sources to power lights around the world. The good news is lighting is getting more efficient and consuming less energy; the bad news is more lighting is being added every day. The move from incandescent light bulbs to compact florescent light bulbs is helping reduce energy use and greenhouse gas emissions, and LED lights will accelerate those savings in the not-too-distant future.

At Walmart, that future is now. Because electricity is the number two operating expense in almost every one of our stores and clubs around the world, we have been focused for decades on efficiency and reducing energy use, particularly from lighting. In 2005 we discovered a game changer when we installed our first LED freezer case lights at a store in McKinney, Texas. We found that these LEDs use approximately 70 percent less energy, create much less heat (important in a freezer case) and last about as long as the cases do - saving money on both energy and maintenance costs. LED freezer case lighting is now the standard in all new Walmart facilities around the globe, and this technology is quickly becoming the norm in the industry. Whether you're in a supermarket in Australia or a hypermarket in South Africa, you're likely to find LED lights in the freezer cases.

LED freezer case lighting is a tremendous success story, but it's still a niche application. If you don't own a grocery store or convenience store, you don't have much use for the technology. Our next focus for LEDs has the potential to impact every business with a parking lot and every community with street lights around the world - LED parking lot lights.

Here's the same lot as above before the LED installation. Photo: Walmart Stores.

Walmart's first full-scale test of LED parking lot lights was at a Neighborhood Market in Rogers, Ark., in 2008. We found the same benefits - big energy and maintenance savings - and some new ones. LEDs are directional, meaning we can better focus the light on our parking lots and limit nighttime glare. Gradually, we began rolling out LED parking lot lights in our international markets that have the highest energy costs. We converted 22 sites in Puerto Rico, saving more than 8 million kilowatt hours of energy in 2009, and we are in the process of converting 350 stores in Central America. Our operations in Mexico also began implementing this technology last year and just in the last few weeks our U.S. program has specified LED lighting as a solution for new store parking lots going forward.

This program also helps export America's "green" technology. Nearly all the LED parking lot light fixtures we use are manufactured by General Electric in its Hendersonville, N.C., facility and sent to our operations outside the U.S.

The biggest challenge that limits Walmart, or any other company, from installing LEDs in parking lots on a large scale is the technology's initial cost. The lamps cost quite a bit more than traditional lighting, and even after calculating all the savings, it still takes years to recover our initial investment (length varies by market). This issue will diminish as the technology improves, and just like we did with freezer case lights, we will use our global scale to help develop this technology and reduce costs. .

General overhead lighting is the next logical step for LED technology and, while it may be a few years away from being a viable option on a large scale, we are testing the technology in our Walmart China stores. To give you an idea of what that looks like, imagine a long light tube covered with hundreds of LED lights. It's a pretty cool sight. We think the potential environmental and business benefits of this application will eclipse what we are realizing with parking lot LEDs.

Light bulbs and fixtures might not be the sexiest innovation in sustainability, but few ideas offer the enormous potential. Every business, every government, every individual uses lights - that's why Walmart is throwing its scale behind the development of technology that uses up to 70 percent less energy and lasts five to six times longer. Just think about the energy and greenhouse gas savings and waste reduction possibilities. At Walmart we have already seen this happen in freezer cases, we're watching it happen in parking lots and we believe the same will happen with general use lighting.